The present invention relates to a device for forming and metering an air and fuel mixture to the manifold of an internal combustion engine, of the type comprising an electromagnetic fuel metering and atomizing valve for supplying predetermined fuel quantities in the form of atomized particles.
Devices of the aforementioned type are generally known to comprise a body, in which is formed a chamber in which atomized fuel is mixed with air, and a cylindrical mixture delivery duct, the opening of which is controlled by a circular throttle valve.
Such devices also comprise a body cover in which are formed a duct and a seat for fuel injector, for supplying air and fuel respectively into the said mixing chamber. The said cover is usually also fitted with a pressure regulator for maintaining constant pressure of the fuel supplied by the injector.
Devices of the aforementioned type present a number of drawbacks.
A major shortcoming of certain types of the aforementioned devices is that they fail to provide for a perfectly homogeneous air and fuel mixture under all operating conditions, due to the swirling motion inside the mixing chamber being insufficient for homogeneously blending the air and fuel particles. Furthermore, fuel drops are formed on the surface of the throttle valve and the cylindrical duct supplying the mixture to the manifold, thus impairing low-speed performance of the engine and dissipating part of the energy supplied by the injector at the fuel atomizing stage. This is due to the atomized fuel jet being blown by the air stream on to the surfaces of the duct and/or throttle, thus resulting in the formation of fuel drops which, moving irregularly along the cylindrical mixture delivery duct, invariably impair engine performance, particularly at low speed.
Certain types of the aforementioned devices fail to provide for steady supply of the mixture as the throttle is opened, particularly in the case of very samll angles. Also, on such devices, the fuel duct arrangement connecting the fuel intake fitting to the injector and the latter to the pressure regulator is fairly complex, thus resulting in variable load loses, particularly over the duct portion between the injector and pressure regulator, and involving fairly complex, unreliable construction designs. Finally, on devices of the aforementioned type, mixing additional air supplied to a given portion of the delivery duct downstream from the throttle, at idling speed or for cold starting of the engine, also involves a number of problems. The said additional air is known to be supplied by a bypass connecting an air intake hold in the device cover to the said delivery duct portion; the said delivery duct usually being provided with a plugging member controlled by an actuator. The location at which the said bypass comes out inside the mixture delivery duct invariably prevents homogeneous mixing of the said additional air with the mixture itself.